Premier Gladys Berejikjlian, who is facing difficult by-elections in the seats of North Shore and Manly, last week committed to building a tolled motorway tunnel linking Balgowlah to the Warringah Freeway.

Ms Berejiklian revealed the preferred route for the "Beaches Link" project and the number of affected properties.

Cronulla MP and Attorney-General Mark Speakman is understood to have lobbied heavily within the government before the announcement to ensure the F6 extension was not delayed by the north shore initiative.

Ms Berejiklian’s office provided no reassurance on the matter, referring questions from the Leader to new Roads Minister Melinda Pavey.

A spokesman for Ms Pavey also avoided the question of priority.

“The NSW Government is continuing geotechnical and traffic studies to plan for a future extension of the F6 in Southern Sydney,” he said.

“The 2016-17 budget included $11.6 million to allow this work to proceed.

“The government has committed $300 million to the Gateway to the South program to bust congestion in the short term.”

Mr Speakman would not comment on any discussions he may have had within the government, but said, since 2011, a total of $46 million had been allocated for planning the F6 extension.

He and other Liberal MPs along the corridor wanted construction to start as soon as possible.

“I would expect a decision at the end of this year or in 2018 when these investigations are done,” he said.

“These investigations will inform the precise route and which of it is in tunnel, where the entry and exit ramps will go and whether it’s built in one go or in stages.”

Mr Speakman said a study that was completed in 2016 rejected an alternative route through Menai.